In the related art, a seat for an automobile has been known which is configured to engage a seat back with a vehicle side part and to thus fix a backrest angle. An example of such seat is disclosed in JP-A-2011-042269. Specifically, a lower end portion of the seat back is shaft-coupled to a base on a floor and a lock device provided at a shoulder part of a vehicle outer side is locked to a striker provided at the vehicle side part, so that the backrest angle is fixed. The striker is attached to a slide, which is provided at the vehicle side part to be slidable in backward and forward direction, and a position at which the backrest angle of the seat back is fixed can be adjusted by changing a fore-and-aft position of the slider.
In the above described related art, the slider is provided at the vehicle side part so that it can straightly slide. For this reason, there may be necessary to provide the lock device or striker with a relief structure for absorbing a difference from a trajectory along which the seat back tilts about a lower end-side axis, which makes the structure complicated. Also, if the lock device is made to have a simple configuration where a pin is simply inserted into a hole provided at the vehicle side part, it is possible to set a position of the hole to a position following the tilting trajectory of the seat back. However, it is difficult to sufficiently obtain the lock strength and to finely set a pitch of the lock.